1. The Field of the Invention
This invention relates to fixators. In particular, this invention relates to external fixators (frames) commonly employed for the orthopedic stabilization of long bones during fracture management or deformity correction.
2. The Relevant Technology
Bone fixators have existed for many years. In a simple embodiment, fixators are plates which span a fissure, fracture or surgically divided bone in order to hold each bone portion in a proper relative position for healing.
In more complex conceptions, such as the Ilizarov type fixator, an external frame is used, together with pins, called “half-pins”, which enter the opposing ends of the bone, in order to stabilize the bone by virtue of the rigid, external frame to which the pins are fixed.
Standard half pins employed for fixation of long bone fragments are typically threaded to engage both sides of the bone and prevent slippage. Prior to insertion, a hole must first be drilled in the bone. The drill bit is then removed and the half pin inserted. The technique requires the placement of multiple threaded pins through bone fragments. These pins then are anchored to external bars or rings. When desired, the position of the frame may subsequently be adjusted to correct deformities or to gain limb length. The success of this technique is predicated upon a secure interface between each of the pins and the adjacent bone. If one or more pins loosen, stability will be lost and the result may be compromised. Suboptimal pin placement may result in pin loosening or breakage or stress fracture of the bone requiring secondary surgery.
External fixators have become ubiquitous in orthopedic trauma and reconstructive surgery. Despite the wide variety of fixators on the market, the common denominator requires the placement of half pins transversely through both sides (cortices) of the bone. These pins are then clamped to the external ring or bar fixators. It is commonplace to apply three pins per bone segment in order to adequately preserve alignment and bone stability. Transverse pins have the potential disadvantage of being subject to failure due to the considerable and repetitive bending stresses imparted by muscle contraction and by the forces of weight bearing. As a result, the pin/bone interface may become unstable; infection or pin breakage may ensue. Furthermore pins may need to be applied at a considerable distance from the rings. This requires the construction of a somewhat unwieldy and weighty superstructure in order to adequately secure the pins.
What is needed therefore is a device which permits more secure and versatile fixation of the bone fragments.